How to use a lapping kit

Expecting your rail, mounts and scope to line up perfectly with your barrel may be wishful thinking, but Mike Morton proves that wishes can be granted…

Lapping means removing minute amounts of material from the inside of your scope rings

In a perfect world, the centreline of your scope rings would exactly coincide with the centreline of your bore. That would mean the scope itself was perfectly lined up to deliver optimum accuracy. Even with the best engineering in the world, though, it’s unlikely that all these different components would come together with that degree of perfection. However, there is a way to achieve this: using a lapping kit.

Lapping means removing minute amounts of material from the inside of your scope rings. The process will help align your rings to the bore of your rifle, and will also align the rings to each other to obtain a near-perfect no-pressure fit for your scope. Lapping will also eliminate imperfections on the rings’ inner surfaces, allowing them to apply a more even force over the contact area with the scope tube. This minimises the risk of the scope shifting in the rings and stops it from getting scratched, which can be a deal-breaker if you want to sell the scope later.

The alignment bars reveal a bit of work is needed here

HIT OR MYTH?

Two myths must be dispelled here. The first is that scope lapping is only of use for long-range centrefire shooters. The point of lapping is to ease any stress on the scope and its components, allowing it to do its job the way it was designed. This is as necessary for air rifles as it is for fullbores. The second myth is that lapping is required only when using cheap scope mounts. Well-made components will benefit from this treatment too. While the process is fairly simple, lapping kits are not cheap: if all that was required was to use better-quality mounts, there would be no need for lapping, and that’s just not the case.

The most popular lapping kits are made by Wheeler Engineering and Sinclair International, but my set comes from Kokopelli Products (www.kokopelliproducts.com). The set contains two bars and a rod to check alignment, as well as a lapping bar and compound.

It goes without saying that you should check to make sure your airgun is safe before carrying out any work on it. You’ll also need to secure it firmly, using something like the MTM gun cradle you can see in our photos.

Secure your rifle and install the lower rings as normal, then use cling-film to wrap the rest of your gun. Take care to use plenty of cling-film around the base of the rings to prevent lapping compound from seeping into your action.

With the gun protected, install the alignment bars and secure the upper rings with the ends of the bars nearly touching. You’ll be able to see instantly whether or not your rings are in alignment with one another. The purpose of this exercise is to check, not to correct. Do not try to use the alignment bars as a tool to bend the mounts straight! That’s what the lapping bar is for. Even if the alignment bars show perfect alignment, the rings will still benefit from lapping as you are evening out the inner surfaces for more secure scope clamping.

Do all you can to keep lapping compound away from your gun. Cling-film is perfect for this. Use smooth, even strokes with the bar, rotating it as you go. The trick is to remove the right amount of material – not too much

RING THE CHANGES

It’s now time to take off the upper rings, remove the alignment bars and prepare the lapping bar. Some bars are smooth, in which case you should add lapping compound to the insides of the rings. The Kokopelli bar is grooved, which means you can load the bar itself with compound. Try not to use more than you need, as things can get messy, and you can easily add more compound during the procedure if necessary.

Lay the lapping bar into the lower rings and add the uppers, snugging down the screws just enough so the bar is making contact with the upper rings, but is still free to move. Once the lapping process has begun, it’s important to treat the rings as single components, always keeping the same upper and lower together, and making a note of the orientation of each.

When you start to lap, the idea is to remove excess material from as much of the inner surface of the rings as possible, so instead of just moving the lapping bar backwards and forwards, twist it clockwise then anti-clockwise as you go. Try to get into a rhythm as you do this: your work will proceed faster and the end result will be more even.

After a few strokes, the bar should feel freer as it runs through the rings. While it’s tempting to keep going, and maybe even increase the pace now it’s becoming easier, stop what you’re doing and check your progress. You’ll need to wipe off the compound and inspect your work. The aim is not to remove an entire layer of material, just the high spots, with no more than 75% of the inner surface being lapped.

The alignment bars prove what a positive impact lapping has had on these mounts

RINSE AND REPEAT

When you’re ready, load more compound onto the bar if needed, and tighten the upper rings, again making sure there is some friction while allowing the bar to move. Stopping, removing the upper rings, removing the lapping bar and cleaning up excess compound all takes time, but it’s important to carry out this process regularly to make sure you remove just the right amount of material, not too much.

When you can see you’ve skimmed off 75% of the inner surfaces, do a thorough clean-up then reinsert the alignment bars and upper rings, this time securing the rings to their normal torque. Not only will the lapping process have increased the clamping area on the inside of the rings, it will also have made them more concentric to one another. If the bars are not perfectly aligned, you have more work to do, and the process begins again.

Compare a lapped ring with a brand new one – the missing finish shows where a high spot has been removed

IS IT ALL WORTH IT?

Lapping may appear to be a lot of effort for minimal return, but it’s a long-term investment in your scope and rifle’s ability to maintain accurate shooting over time, particularly if you’re shooting a springer or gas ram.

The vibration from any recoil is constantly trying to shift your scope within the rings. Instead of countering this by clamping down on the scope tube with excessive force, potentially damaging the internals, you are providing a greater surface area inside the rings to grip the scope.

The scope is also lying concentric to the bore, removing any flex from the scope tube and making it more optically centred, giving you a greater range of turret adjustment into the bargain. Lapping increases the likelihood of your combo holding zero with extended use, and that’s got to make the whole process worthwhile.

Lapping may appear to be a lot of effort for minimal return, but it’s a long-term investment in your scope

LET’S GET READY TO RUMBLE

1. Lapping compound contains abrasive particles that can easily cut steel, let alone aluminium. Keep it away from your rifle at all costs. Cling-film or aluminium foil are ideal for this task.

2. Keep plenty of paper towels on hand. You’ll need to wipe away excess compound to check your progress as you go as well as to clean up afterwards.

3. Brake cleaner is an ideal solvent to clean up lapping compound. It’s best used outdoors. Try not to breathe it in, and keep it away from your eyes.

4. Latex gloves will keep your hands clean of the compound and protect them from the solvent. Brake cleaner can irritate sensitive skin.


This article originally appeared in the issue 100 of Airgun Shooter magazine. For more great content like this, subscribe today at our secure online storewww.myfavouritemagazines.co.uk

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Posted in Features, How to

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